Summer of Fear by Lois Duncan

Rachel has the perfect life–a great family, a cute and attentive boyfriend, a best friend who’s like a sister to her, and the real love of her life—her dog Trickle. Then Rachel’s cousin Julia moves in. Rachel is prepared to do anything for Julia–after all, Julia’s parents, Rachel’s aunt and uncle, just died in a horrible car accident and Rachel wants Julia to try and feel at home despite her enormous loss. What Rachel wasn’t expecting is how “at home” Julia becomes–to the point of stealing her best friend and cozying up to her boyfriend. Trickle is the only other family member that dislikes Julia as much as Rachel–as Julia soon takes care of that as well! Rachel is afraid that Julia won’t stop until she has stolen Rachel’s entire life! But that doesn’t make Julia a witch…does it? If all you know of Lois Duncan is her book I Know What You Did Last Summer, then you don’t know her at all. Her teen thrillers are supreme–don’t miss out on this one or any of her other titles.